1. Field of the Invention
This invention relates to bone fixation and compression devices.
2. Discussion of Related Art
Numerous intramedullary devices have been proposed in the past for providing both internal fixation of bone fractures as well as compression of the bone fragments at the fracture site. The normal procedure for fracture reduction when using such an intramedullary device includes drilling out a portion of the medullary canal in both the distal and proximal portions of the fractured bone. The intramedullary device is then inserted into the drilled out sections and engages the bone to draw the bone halves together. The manner of engagement between the device and the bone itself is extremely critical in that the means for engagement must provide both axial and radial stability of the bone segments. A major failing of prior intramedullary devices inheres in their failing to provide an effective engagement which both insures against radial and axial displacement of the bone halves and at the same time provides even pressure distribution to insure against bone splitting or pressure insult to the bone.
U.S. Pat. No. 3,717,146, issued Feb. 20, 1973, to Halloran, shows an intramedullary compression pin which includes conical threaded ends which are driven into the distal and proximal portions of the fractured bone and engage the cancellous bone to, in effect, tap the medullary canal and draw the rod into the bone halves. U.S. Pat. No. 3,846,846, issued Nov. 12, 1974, to Fischer, shows a hip joint prosthesis which is held in place through the use of a rod inserted in the medullary cavity of the bone and surrounded by a plurality of expansion elements. Adjacent expansion elements are telescopingly received with each inner element causing radial pressure forcing the adjacent outer element into the wall of the medullary canal. U.S. Pat. No. 4,091,806, issued May 30, 1978, to Aginsky, shows an intramedullary compression nail which includes a bolt head extending from one end of a fractured bone. The bolt extends through a sleeve having a bifurcated free end. The bifurcations are caused to separate by a threaded follower which is drawn along the bolt within the sleeve. The diverging bifurcated portions are forced into the walls of the medullary canal. U.S. Pat. No. 3,990,438, issued Nov. 9, 1976, to Pritchard, shows a bone fracture fixation and compression apparatus having a first portion containing cutting threads for anchoring within the principal bone. The other end of the device threadedly engages a screw which extends outward of the bone and is forced against the end of the bone for producing axial compression.